The present invention relates to methods and compositions for treating subterranean formations. More particularly, the present invention relates to treatment fluids that comprise a weakly emulsifying (“WE”) surfactant, and associated methods.
Treatment fluids may be used in a variety of subterranean treatments. Such treatments include, but are not limited to, stimulation treatments and enhanced or improved oil recovery operations. As used herein, the term “treatment,” or “treating,” refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The term “treatment,” or “treating,” does not necessarily imply any particular action by the fluid.
One common production stimulation operation that employs a treatment fluid is hydraulic fracturing. Hydraulic fracturing operations generally involve pumping a treatment fluid (e.g., a fracturing fluid) into a well bore that penetrates a subterranean formation at a sufficient hydraulic pressure to create or enhance one or more cracks, or “fractures,” in the subterranean formation. The fracturing fluid may comprise particulates, often referred to as “proppant particulates,” that are deposited in the fractures. The proppant particulates function, inter alia, to prevent the fractures from fully closing upon the release of hydraulic pressure, forming conductive channels through which fluids may flow to the well bore. Once at least one fracture is created and the proppant particulates are substantially in place, the viscosity of the fracturing fluid usually is reduced, and the fracturing fluid may be recovered from the formation.
Another production stimulation operation that employs a treatment fluid is an acidizing treatment. In acidizing treatments, subterranean formations comprising acid-soluble components, such as those present in carbonate and sandstone formations, are contacted with a treatment fluid comprising an acid. For example, where hydrochloric acid contacts and reacts with calcium carbonate in a formation, the calcium carbonate is consumed to produce water, carbon dioxide, and calcium chloride. After acidization is completed, the water and salts dissolved therein may be recovered by producing them to the surface, e.g., “flowing back” the well, leaving one or more voids (e.g., wormholes) within the formation, which enhance the formation's permeability and may increase the rate at which hydrocarbons may subsequently be produced from the formation. One method of acidizing, known as “fracture acidizing,” comprises injecting a treatment fluid comprising an acid into the formation at a pressure sufficient to create or enhance one or more fractures within the subterranean formation. The acid treatment fluid may leave one or more voids within the formation in addition to the one or more fractures enhanced within the formation. Another method of acidizing, known as “matrix acidizing,” comprises injecting the treatment fluid into the formation at a pressure below that which would create or enhance one or more fractures within the subterranean formation. This acidizing method may likewise leave one or more voids within the formation.
Surfactants are widely used in stimulation operations, including hydraulic fracturing and acidizing (both fracture acidizing and matrix acidizing) treatments. Surfactants may also be used in enhanced or improved oil recovery operations. Many variables may affect the selection of a surfactant for use in such treatments and operations, such as interfacial surface tension, wettability, compatibility with other additives (such as other additives used in acidizing treatments), and emulsification tendency. Many conventional treatments and operations such as hydraulic fracturing and acidizing treatments utilize non-emulsifying (“NE”) surfactants in order to avoid the formation of tight emulsions between the oil and aqueous phases within a formation. Tight emulsions are thought to block the oil and gas flow by plugging the pore throats, voids, fractures, or other channels in the formation. This formation damage could drastically reduce production from the formation.
However, the use of NE surfactants in stimulation operations such as acidizing treatments may result in sub-optimal oil and/or gas flow from the formation.
While the present invention is susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit or define the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. The figures should in no way be used to limit the meaning of the claim terms.
The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the preferred embodiments that follows.